This invention concerns improvements in or relating to optical apparatus and relates more particularly to optical apparatus for biocular viewing of a magnified image of a distant scene or object especially under daylight conditions.
There have been previous proposals for biocular magnifying lenses through which an observer can view simultaneously with both eyes a magnified image of an object. These have been proposed, in particular, for low light level or night vision devices in which the viewed object is located close to the lens and takes the form, for example, of a cathode ray tube or the phosphor of an image intensifier. It has been found that one problem with such lenses is that generally only a small fraction of the light travels to the observer's pupils because of his spaced eye positions, the cones of rays generating such used light being at a considerable angle to the optical axis. It has further been found that, for this reason, such biocular magnifying lenses are not generally immediately applicable to the daylight viewing of distant scenes or objects by simply associating them with an objective lens because the aerial image formed by an objective lens usually has only a relatively narrow cone of light which tends to pass between the eyes, rather than entering them, of an observer attempting to view the image through such a biocular magnifying eyepiece lens.